1. Field of the Invention
This invention relates, in general, to communication systems for electrical power lines and, more specifically, to apparatus for supplying power to communication amplifiers or repeaters connected to the primary portions of a power distribution system.
2. Description of the Prior Art
Communication signal amplifiers or repeaters are used in power line carrier communication systems to compensate for attenuation of the communication signal along the power line. such signal amplifiers or repeaters usually include electronic circuitry which requires electrical power for its operation. Although many arrangements have been proposed, one of the most practical methods involves acquiring electrical energy from the power line system to which it is associated.
When the signal amplifiers or repeaters are connected to the secondary or low-voltage portion of the power distribution lines, the electrical power for operating the amplifier can be obtained directly from the secondary portion of the distribution system. However, when the amplifier is associated with the high-voltage or primary portion of the distribution system, extreme care must be used when delivering power to the amplifier from a secondary or low-voltage line. This is due mainly to the possibility that high-voltage surges on the primary portion of the distribution line may be conducted to the secondary portion of the distribution line through the apparatus which powers the signal amplifier. Consequently, such power arrangements must provide complete isolation between the primary and secondary power line systems under severe voltage surge conditions.
To eliminate the need for isolation between the apparatus which supplies power to the amplifier and the high potential on the distribution line, some arrangements have used apparatus which divides or reduces the voltage of the high-voltage distribution line to that suitable for powering the signal amplifier. One such arrangement uses a series network of capacitors connected between the high-voltage line and ground potential. The capacitor arrangement acts as a capacitive voltage divider circuit and provides a reduced voltage to the signal amplifier. Another arrangement uses a step-down transformer which is connected between the high-voltage line and ground potential and is connected to the signal amplifier. Although both arrangements have been used in practical applications, the requirement that the components used therein be suitable for use at extremely high potentials increases the cost of such apparatus.
Therefore, it is desirable, and it is an object of this invention, to provide an arrangement for powering a signal amplifier connected to the primary portion of a power distribution line, with such arrangement providing an economical and reliable means for supplying power to the signal amplifier while still maintaining isolation between the primary and secondary conductors of the power distribution system.